This is not inconsistent with the claim that, if the country of rationalists is attacked by a country of barbarians who are imperfectly optimized for conquest, the rationalists might get conquered, with the risk depending on how optimized the barbarians are.

How imperfectly optimized, though? Imperfectly optimized like Omega controlling each barbarian but occasionally rolling the barbarian's morale check, which fails on a 1 on a D100? Or imperfectly optimized like real life barbarians?